Image forming apparatus and image forming method

ABSTRACT

In accordance with an embodiment, an image forming apparatus comprises a printing setting acquisition section and a printer section. The printing setting acquisition section acquires printing setting information for holding setting at the time of printing for each kind of a sheet. The printer section applies, in a case in which a label paper is selected as the kind of the sheet, a developing agent in the vicinity of an area coming into contact with an end part of the sheet in an area on an image carrier for transferring the developing agent to the sheet, transfers the developing agent by a transfer member for transferring the developing agent from the image carrier to the sheet, and rotates the transfer member at least once.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 15/709,789filed on Sep. 20, 2017, the entire contents of which are incorporatedherein by reference.

FIELD

Embodiments described herein relate generally to an image formingapparatus and an image forming method.

BACKGROUND

In recent years, various types of media such as a label paper, plasticmedia such as an OHP, a sheet with the surface of a paper coated, inaddition to a normal sheet, is printed in an image forming apparatus.

However, in the case of media including an adhesive layer such as alabel paper, if heat and pressure are applied to the media, an adhesiveagent of the adhesive layer adheres to an image carrier, a fixing deviceand a conveyance path. The adhering adhesive agent is not sufficientlyremoved by a cleaner for removing remaining toner on the image carrier.Thus, there is a case in which cleaning failure occurs, and problemssuch as conveyance failure and image failure occur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external view illustrating an example of an entireconstitution of an image forming apparatus 100 according to anembodiment;

FIG. 2 is a diagram illustrating one concrete example of a constitutionof a label paper;

FIG. 3 is a functional block diagram illustrating functional componentsof the image forming apparatus 100 according to the embodiment;

FIG. 4 is a diagram illustrating an inner constitution of a printersection 130 according to the embodiment;

FIG. 5 is a diagram illustrating one concrete example of a visible imageformed in the vicinity of an edge of an end part of the label paperaccording to the embodiment;

FIG. 6 is a diagram illustrating a positional relationship in a widthdirection in a case in which portions of both sides of the label paperare secondarily transferred according to the embodiment;

FIG. 7 is a diagram illustrating one concrete example of a relationshipbetween lengths of widths of respective members according to theembodiment;

FIG. 8 is a diagram illustrating one concrete example of biasapplication to a secondary transfer counter roller 144 according to theembodiment;

FIG. 9 is a flowchart illustrating cleaning of a secondary transferroller 143 according to the embodiment;

FIG. 10 is a diagram illustrating one concrete example in which ahalftone visible image is formed on an end part of the label paperaccording to the embodiment;

FIG. 11 is a diagram illustrating one concrete example of biasapplication in a case in which toner charged to a positive polarity isremoved according to the embodiment; and

FIG. 12 is a diagram illustrating one concrete example of an innerconstitution of a printer section of a monochrome image formingapparatus.

DETAILED DESCRIPTION

In accordance with an embodiment, an image forming apparatus comprises aprinting setting acquisition section and a printer section. The printingsetting acquisition section acquires printing setting information forholding setting at the time of printing for each kind of a sheet. Theprinter section applies, in a case in which a label paper is selected asthe kind of the sheet, a developing agent in the vicinity of an areacoming into contact with an end part of the sheet in an area on an imagecarrier for transferring the developing agent to the sheet, transfersthe developing agent by a transfer member for transferring thedeveloping agent from the image carrier to the sheet, and rotates thetransfer member at least once.

FIG. 1 is an external view illustrating an example of an entireconstitution of an image forming apparatus 100 according to anembodiment. The image forming apparatus 100 is, for example, amulti-functional peripheral. The image forming apparatus 100 includes adisplay 110, a control panel 120, a printer section 130, a sheet housingsection 140, and an image reading section 200. Furthermore, the printersection 130 of the image forming apparatus 100 may be a device forfixing a toner image.

The image forming apparatus 100 forms an image on a sheet with adeveloping agent such as toner. The sheet is, for example, a paper or alabel paper. The sheet may be an optional sheet as long as the imageforming apparatus 100 can form an image on the surface of the sheet.

The display 110 is an image display device such as a liquid crystaldisplay, an organic EL (Electro Luminescence) display and the like. Thedisplay 110 displays various kinds of information relating to the imageforming apparatus 100.

The control panel 120 has a plurality of buttons. The control panel 120receives an operation of a user. The control panel 120 outputs a signalcorresponding to an operation carried out by the user to a controlsection of the image forming apparatus 100. Furthermore, the display 110and the control panel 120 can be separate or both may be integrated intoa single touch panel.

The printer section 130 forms an image on a sheet on the basis of imageinformation generated by the image reading section 200 or imageinformation received via a communication path. The printer section 130forms the image through, for example, the following processing. Theimage forming section of the printer section 130 forms an electrostaticlatent image on a photoconductive drum 149 on the basis of the imageinformation. The image forming section of the printer section 130enables a developing agent to adhere to the electrostatic latent imageto form a visible image. As a concrete example of the developing agent,toner is exemplified. The transfer section of the printer section 130transfers the visible image on the sheet. The fixing section of theprinter section 130 heats and pressures the sheet to enable the visibleimage to be fixed on the sheet. Furthermore, the sheet on which theimage is formed may be a sheet housed in the sheet housing section 140or a manually fed sheet.

The sheet housing section 140 houses a sheet used for printing by theprinter section 130.

The image reading section 200 reads the image information of a readobject as intensity of light. The image reading section 200 records theread image information. The recorded image information may be sent toanother information processing apparatus via a network. The recordedimage information may be printed on the sheet by the printer section130.

FIG. 2 is a diagram illustrating one concrete example of a constitutionof a label paper. The label paper is composed of a release paper, anadhesive layer and a surface layer. The label paper is used by peelingthe surface layer and the adhesive layer from the release paper. Theadhesive layer is composed of an adhesive agent. The adhesive layeradheres to a substance brought into contact after peeled from therelease paper. If pressure is applied to the adhesive layer, there is acase in which the adhesive agent leaks out from an end part. Theadhesive agent is composed of, for example, a paste. The surface layeris a printing surface of the label paper.

FIG. 3 is a functional block diagram illustrating functional componentsof the image forming apparatus 100 according to the embodiment. Theimage forming apparatus 100 includes a communication section 101, aprinting setting storage section 102, a control section 103, the controlpanel 120, the printer section 130 and the image reading section 200.

The communication section 101 is a network interface. The communicationsection 101 communicates with an external terminal via a network. Thecommunication section 101 may carry out communication by a communicationsystem, for example, an LAN (Local Area Network), a PSTN (PublicSwitched Telephone Network) or a NFC (Near Field Communication)

The printing setting storage section 102 is constituted using a storagedevice such as a magnetic hard disk device or a semiconductor storagedevice. The printing setting storage section 102 stores printing settinginformation. The printing setting information holds setting of theprinter section 130 in a case in which print media such as sheets andmedia are printed. The printing setting storage section 102 stores theprinting setting information for each of print media. The printingsetting information has information, for example, rotational speeds ofvarious rollers, which cassette of the sheet housing section 140 a sheetis acquired from, and the like. In a case in which the printing settinginformation is information in which print media relate to a label paper,the printing setting information has setting for forming a toner patternon an end part of the label paper.

The control section 103 controls operations of each section of the imageforming apparatus 100. The control section 103 is executed by, forexample, a device including a CPU (Central Processing Unit) forcontrolling the overall device and a RAM (Random Access Memory). Thecontrol section 103 functions as a printing setting acquisition section104 by executing an image forming program.

The printing setting acquisition section 104 acquires, on the basis ofinstruction information received by the control panel 120, the printingsetting information from the printing setting storage section 102. Theinstruction information includes information (for example, a sheet typeand a sheet size) which can specify any printing setting informationfrom a plurality of printing setting information stored in the printingsetting storage section 102. The printing setting acquisition section104 outputs the acquired printing setting information to the printersection 130. The printing setting acquisition section 104 may receivethe instruction information from an external terminal 300.

The external terminal 300 is an information processing device such as apersonal computer, a tablet computer or a smartphone.

The printer section 130 carries out printing on the basis of theprinting setting information. Specifically, the printer section carriesout printing by controlling an exposure section 131, a photoconductordrive section 132, a developing device mixer drive section 133, adeveloping roller drive section 134, a transfer belt drive section 135,a high voltage power supply section 136, a sheet feed motor 137, a sheetconveyance motor 138, a duplex conveyance motor 139 and a fixing section150.

The exposure section 131 exposes the photoconductive drum 149 byenabling a light emitting element to emit light. The photoconductordrive section 132 rotates the photoconductive drum 149 by driving amotor for the photoconductive drum 149. The developing device mixerdrive section 133 rotates a mixer member in the developing device bydriving a motor for a developing device 151. The developing roller drivesection 134 rotates a developing roller by driving a motor for thedeveloping roller included in the developing device. The transfer beltdrive section 135 rotates an intermediate transfer belt 146 by driving amotor for the intermediate transfer belt 146.

The high voltage power supply section 136 applies biases to a chargingroller, the developing roller, a primary transfer roller 148 and asecondary transfer counter roller 144. The high voltage power supplysection 136 includes a charging bias transformer section 161, adeveloping bias transformer section 162, a primary transfer biastransformer section 163 and a secondary transfer bias transformersection 164.

The charging bias transformer section 161 applies a bias to the chargingroller. The developing bias transformer section 162 applies a bias tothe developing roller. The primary transfer bias transformer section 163applies a bias to the primary transfer roller 148. The secondarytransfer bias transformer section 164 applies a bias to the secondarytransfer counter roller 144.

The sheet feed motor 137 conveys a sheet from the sheet housing section140 to the printer section 130. The sheet conveyance motor 138 conveysthe sheet conveyed from the sheet housing section 140. The duplexconveyance motor 139 conveys, to the secondary transfer roller 143, thesheet conveyed to the fixing section 150, through an ADU section.

The fixing section 150 fixes toner adhering to the sheet on the sheetthrough heat and pressure. The fixing section 150 includes a fixingdevice drive section 151 and a fixing heater 152. The fixing devicedrive section 151 rotates a heating roller 156 and a pressure roller 157included in the fixing section 150 by driving motors of the heatingroller 156 and the pressure roller 157. The fixing heater 152 is builtin the heating roller 156. The fixing heater 152 melts the toner bygenerating heat.

FIG. 4 is a diagram illustrating an inner constitution of the printersection 130 according to the embodiment. The printer section 130according to the embodiment is the form of a quadruple tandemintermediate system. The printer section 130 includes the exposuresection 131, the sheet housing section 140, a sheet feed roller 141, asheet conveyance roller 142, the secondary transfer roller 143, thesecondary transfer counter roller 144, a sheet discharge roller 145, theintermediate transfer belt 146, an intermediate transfer belt cleaner147, the primary transfer roller 148, the photoconductive drum 149, thefixing section 150, the developing device 151, a charger 153, a chargeremoving device 154 and a cleaner 155.

Herein, the primary transfer roller 148, the photoconductive drum 149,the developing device 151, the exposure section 131, the charger 153,the charge removing device 154 and the cleaner 155 are disposed for eachcolor of the developing agents. In the present embodiment, the numbersof foregoing components each are four. Hereinafter, the sheet housed inthe sheet housing section 140 is described as the label paper.

The label paper housed in the sheet housing section 140 is conveyed to aroute 10 by the sheet feed roller 141. The label paper conveyed to theroute 10 is conveyed to a route 11 by the sheet conveyance roller 142.The label paper conveyed to the route 11 is conveyed to a route 12 bythe secondary transfer roller 143. The label paper conveyed to the route12 is conveyed to a route 13 by the heating roller 156 and the pressureroller 157 included in the fixing section 150. The label paper conveyedto the route 13 is discharged to outside of the image forming apparatus100 by the sheet discharge roller 145.

If the label paper is conveyed to the secondary transfer roller 143, thevisible image is transferred by the secondary transfer roller 143. Thevisible image is an image formed on the intermediate transfer belt 146.The visible image also includes a toner pattern also formed in thevicinity of an edge of an end part of the label paper. The visible imageformed in the vicinity of the edge of the end part of the label paper isformed in a paper area and a non-paper area. The intermediate transferbelt 146 is one form of an image carrier for transferring the developingagent to the sheet.

There is a case in which the adhesive agent of the label paper leaks outfrom the end part through the pressure applied from the secondarytransfer roller 143. The leaked adhesive agent comes into contact withthe developing agent transferred in the vicinity of the edge of the endpart of the label paper. The developing agent coming into contact withthe adhesive agent reduces adhesive force of the adhesive agent to theintermediate transfer belt 146. Thus, the most of the leaked adhesiveagent is conveyed to the fixing section 150 together with the labelpaper. The developing agent which is not transferred to the label paperand the adhesive agent slightly adhering to the intermediate transferbelt 146 are removed by the intermediate transfer belt cleaner 147.

FIG. 5 is a diagram illustrating one concrete example of a visible imageformed in the vicinity of an edge of an end part of the label paperaccording to the embodiment. An arrow 14 represents a conveyancedirection of a label paper 400. An area 401 covering an end part of thelabel paper 400 is an area in which a visible image is formed. Thevisible image is formed in the vicinity of the edge of the end part towhich the adhesive agent is easy to leak out. The inner side of thelabel paper 400 within the area 401 is a paper area. The outer side ofthe label paper 400 within the area 401 is a non-paper area. Theadhesive agent is easy to leak out to the non-paper area of the area401.

The visible image is printed in the vicinity of the edge of the end partof the label paper 400. Thus, it is desirable that the visible image isprinted in a color of the surface layer of the label paper. For example,in a case in which the surface layer of the label paper 400 is blue, theprinter section 130 prints the visible image in blue (mixed color of Cand M). In a case in which the label paper 400 is a type of label paperwhich does not use the end part as the label, the printer section 130may increase the density of the visible image formed in the area 401.The visible image may be formed by a white developing agent, a colorlessdeveloping agent or a decoloring developing agent. With such aconstitution, even if the developing agent adheres to the end part ofthe label paper 400, the color can be made inconspicuous. The decoloringdeveloping agent is a developing agent to be decolored through heating.

FIG. 6 is a diagram illustrating a positional relationship in a widthdirection in a case in which portions of both sides of the label paperare secondarily transferred according to the embodiment. An area 401 isan area indicating the developing agent formed on the intermediatetransfer belt 146, similar to FIG. 5. An area 402 is an edge portion ofan end part of the label paper 400. The area 402 is an area to which theadhesive agent is easy to leak out. With reference to FIG. 6, even ifthe adhesive agent leaks out from the label paper 400 to the area 402through the pressure of the secondary transfer roller 143, the adhesiveagent does not adhere to the intermediate transfer belt 146 since thedeveloping agent adhering to the area 401 is shielded.

FIG. 7 is a diagram illustrating one concrete example of a relationshipbetween lengths of widths of respective members according to theembodiment. A width of a printable label paper having a maximum size isa width of the largest label paper that can be printed by the imageforming apparatus. An exposure acceptable width is a width of exposureto the photoconductive drum 149 by the exposure section 131. It isdesirable that the exposure acceptable width is longer than the width ofthe label paper such that the visible image is formed up to thenon-paper area of the label paper.

A developing agent conveyance width is a width capable of forming thevisible image on the intermediate transfer belt 146 by the developingagent. It is desirable that the developing agent conveyance width islonger than the exposure acceptable width such that the visible image isalso formed in the exposed non-paper area. A belt cleaner width is awidth of the intermediate transfer belt cleaner 147 for removing thedeveloping agent left on the intermediate transfer belt 146. It isdesirable that the belt cleaner width is longer than the developingagent conveyance width such that the developing agent on theintermediate transfer belt 146 is removed.

FIG. 8 is a diagram illustrating one concrete example of biasapplication to the secondary transfer counter roller 144 according tothe embodiment. If the visible image is formed in the non-paper area,there is a case in which the developing agent adheres to the secondarytransfer roller 143. If the developing agent adheres to the secondarytransfer roller 143, there is a possibility that the developing agentadheres to the back surface of a subsequent sheet next time. A modulefor preventing that the developing agent adheres to the back surface ofthe sheet is described with reference to FIG. 8. The vertical axisrepresents a polarity of a bias applied to the secondary transfercounter roller 144. The horizontal axis represents passage of time.

In a case in which the value of the vertical axis is smaller than 0, abias of a negative polarity is applied to the secondary transfer counterroller 144. The negative polarity is the same polarity as the developingagent charged quantity. Thus, the developing agent adhering to theintermediate transfer belt 146 repels against the intermediate transferbelt 146, and adheres to the label paper 400.

In a case in which the value of the vertical axis is greater than 0, abias of a positive polarity is applied to the secondary transfer counterroller 144. The positive polarity is an opposite polarity to thedeveloping agent charged quantity. Thus, the developing agent adheringto the secondary transfer roller 143 is attracted to the secondarytransfer counter roller 144, and adheres to the intermediate transferbelt 146.

An arrow 501 represents a length of time when the developing agent istransferred to the label paper. The secondary transfer counter roller144 is applied with the bias of the negative polarity only correspondingto the time shown by the arrow 501. The developing agent is transferredfrom the intermediate transfer belt 146 to the label paper at the timethe bias of the negative polarity is applied.

An arrow 502 represents a length of time when the secondary transferroller 143 is rotated at least one or more times. The secondary transfercounter roller 144 is applied with the positive polarity bias only forthe time shown by the arrow 502. The developing agent moves from thesecondary transfer roller 143 to the intermediate transfer belt 146 atthe time the positive polarity bias is applied. Since the secondarytransfer roller 143 is rotated at least one or more times, thedeveloping agent adhering to the whole surface of the secondary transferroller 143 can move to the intermediate transfer belt 146. Thus, thedeveloping agent adhering to the secondary transfer roller 143 can beprevented from adhering to the back surface of the sheet to be printedsubsequently.

An arrow 503 represents a length of time when the developing agent istransferred to the next label paper. The secondary transfer counterroller 144 is applied with the bias of the negative polarity only forthe time shown by the arrow 503. The developing agent is transferredfrom the intermediate transfer belt 146 to the label paper at the timethe bias of the negative polarity is applied.

FIG. 9 is a flowchart illustrating cleaning of the secondary transferroller 143 according to the embodiment. The printing setting acquisitionsection 104 of the image forming apparatus receives an instruction oflabel paper printing from a user via the control panel 120 (ACT 101).The printing setting acquisition section 104 acquires printing settinginformation relating to the label paper printing from the printingsetting storage section 102 (ACT 102). The printer section 130 of theimage forming apparatus 100 forms a visible image on the intermediatetransfer belt 146 on the basis of the printing setting informationrelating to the label paper printing (ACT 103). At this time, theprinter section 130 forms a visible image on an edge portion of an endpart of the label paper, in addition to the visible image of the imagereceived from the user.

The label paper is pressured by the secondary transfer roller 143 andthe secondary transfer counter roller 144 such that the visible image onthe intermediate transfer belt 146 is transferred to the label paper(ACT 104). At this time, there is a case in which the developing agentadheres to the secondary transfer roller 143.

The developing agent adhering to the secondary transfer roller 143 movesto the intermediate transfer belt 146 (ACT 105). Specifically, thesecondary transfer bias transformer section 164 applies the bias of thepositive polarity to the secondary transfer counter roller 144. Thesecondary transfer counter roller 144 attracts the developing agentadhering to the secondary transfer roller 143, and enables thedeveloping agent to adhere to the intermediate transfer belt 146. Theintermediate transfer belt cleaner 147 removes the developing agentadhering to the intermediate transfer belt 146 (ACT 106).

In the image forming apparatus 100 constituted in this way, the visibleimage is formed in the non-paper area of the edge portion of the endpart of the label paper 400. The adhesive force of the adhesive agentleaked out from the label paper 400 is reduced by the visible image.Thus, the adhesive agent can be prevented from adhering to theintermediate transfer belt 146. Further, by adding the developing agentadded to the edge portion of the end part of the label paper 400, suchas the white developing agent, the colorless developing agent or thedecoloring developing agent, even if the surface layer of the labelpaper 400 is white, the visible image can be made inconspicuous.Moreover, after the label paper is printed, the developing agentadhering to the intermediate transfer belt 146 can be removed byapplying the bias of the positive polarity to the secondary transfercounter roller 144. Thus, the developing agent adhering to the secondarytransfer roller 143 can be prevented from adhering to the back surfaceof the sheet to be printed subsequently.

(Modification)

FIG. 10 is a diagram illustrating one concrete example in which ahalftone visible image is formed on the end part of the label paperaccording to the embodiment. An area 401 a is an area indicating thedeveloping agent formed on the intermediate transfer belt 146. An amount(like halftone) of the developing agent of the paper area coming intocontact with the label paper 400 in the area 401 a may be less than thatof the non-paper area. With such a constitution, even if the mixed coloris not used such that the surface layer of the label paper 400 is white,the visible image of the edge portion of the end part of the label paper400 can be made inconspicuous. Furthermore, in a case in which thesurface layer of the label paper 400 is white, it is desirable to formthe visible image with inconspicuous yellow toner. However, in the caseof the image forming apparatus in which the yellow toner cannot be used,a thin halftone visible image may be used in the paper area.

FIG. 11 is a diagram illustrating one concrete example of biasapplication in a case in which toner charged to the positive polarity isremoved according to the embodiment. The developing agent is charged tothe negative polarity in most cases. However, according to the usecondition of the developing agent, there is a case in which a part ofthe developing agent is charged to the positive polarity. The developingagent charged to the positive polarity cannot move from the secondarytransfer roller 143 to the intermediate transfer belt 146 in the methoddescribed in FIG. 8.

Herein, in FIG. 11, a method for changing the bias applied to thesecondary transfer roller 143 is changed alternately at a predeterminedtime. Herein, the predetermined time is time when the secondary transferroller 143 is rotated at least one or more times. The vertical axisrepresents a polarity of a bias applied to the secondary transfercounter roller 144. The horizontal axis represents passage of time.Points different from FIG. 8 are described.

An arrow 504 represents time when the developing agent of the positivepolarity moves from the secondary transfer roller 143 to theintermediate transfer belt 146. A length of the time represented by thearrow 504 represents a length of time when the secondary transfer roller143 is rotated at least one or more times. The secondary transfercounter roller 144 is applied with the bias of the negative polarityonly for the time shown by the arrow 504. The developing agent of thepositive polarity moves from the secondary transfer roller 143 to theintermediate transfer belt 146 at the time the bias of the negativepolarity is applied. Since the secondary transfer roller 143 is rotatedat least one or more times, the developing agent of the positivepolarity adhering to the whole surface of the secondary transfer roller143 can move to the intermediate transfer belt 146. With such aconstitution, the developing agent adhering to the secondary transferroller 143 moves to the intermediate transfer belt 146, and thus can beprevented from adhering to the back surface of the sheet to be printedsubsequently.

Further, the image forming apparatus 100 may be constituted such that acleaning blade abuts against the secondary transfer roller 143. Withsuch a constitution, the developing agent adhering to the secondarytransfer roller 143 can be removed more certainly, and can be preventedfrom adhering to the back surface of the sheet to be printedsubsequently.

The present embodiment has a printer section as shown in FIG. 12, andmay be applied to a monochrome image forming apparatus. The printersection of the monochrome image forming apparatus includes an exposuresection 131 a, a transfer roller 143 a, a cleaning blade 147 a, aphotoconductive drum 149 a, a developing device 151 a and a chargingroller 153 a. An arrow 14 is a conveyance direction of a label paper. Inthe monochrome image forming apparatus, the exposure section 131 afunctions as the exposure section 131 according to the embodiment. Inthe monochrome image forming apparatus, the transfer roller 143 afunctions as the secondary transfer roller 143 according to theembodiment. In the monochrome image forming apparatus, the cleaningblade 147 a functions as the intermediate transfer belt cleaner 147according to the embodiment. In the monochrome image forming apparatus,the photoconductive drum 149 a functions as the intermediate transferbelt 146 and the secondary transfer counter roller 144 according to theembodiment. However, the monochrome image forming apparatus cannot applya transfer bias from the photoconductive drum 149 a side. In this case,the monochrome image forming apparatus applies the transfer bias havingthe opposite polarity to a charged polarity of the developing agent fromthe transfer roller 143 a side and transfers the visible image to thelabel paper. In the monochrome image forming apparatus, the developingdevice 151 a functions as the developing device 151 according to theembodiment.

In the monochrome image forming apparatus, the visible image formed onan edge portion of an end part of the label paper adheres to thetransfer roller 143 a. Thus, the developing agent can move from thetransfer roller 143 a to the photoconductive drum 149 a by applying abias of a cleaning polarity to the transfer roller 143 a. The cleaningpolarity is the same polarity as the charged polarity of the developingagent. The developing agent adhering to the photoconductive drum 149 ais removed by the cleaning blade 147 a.

With such a constitution, the developing agent adhering to the transferroller 143 a can be prevented from adhering to the back surface of thesheet to be printed subsequently.

While certain embodiments have been described these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms: furthermore variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the invention.

What is claimed is:
 1. An image forming apparatus, comprising: a printer configured to form a toner image on a photosensitive drum; a transfer device including transfer roller configured to transfer the toner image formed on the photosensitive drum onto a label sheet; a controller configured to form the toner image on the photosensitive drum by the printer, the photosensitive drum having a width which extends over a width of the label sheet and configured to transfer the toner image onto the label sheet; and a supply device configured to supply another label sheet to the transfer device after a time passes necessary for the transfer roller to perform at least one rotation after the transfer of the toner image onto the label sheet.
 2. The image forming apparatus according to claim 1, wherein the printer transfers a developing agent to the label sheet, and applies a bias in an opposite direction to that when the transfer device transfers the toner image to the label sheet.
 3. The image forming apparatus according to claim 1, wherein the printer transfers a developing agent to the label sheet, applies a bias in an opposite direction to that when the transfer device transfers the toner image to the label sheet, and further applies a bias in the same direction as that when the transfer device transfers the toner image onto the label sheet.
 4. The image forming apparatus according to claim 1, wherein the printer adds a smaller amount of a developing agent than an area beyond the label sheet to an area at least within the label sheet in the vicinity of the area on the toner image coming into contact with the end part of the label sheet.
 5. The image forming apparatus according to claim 4, wherein the printer adds a developing agent such that a halftone visible image is formed in the area within the label sheet in the vicinity of the area on the toner image coming into contact with the end part of the label sheet.
 6. The image forming apparatus according to claim 5, wherein the printer adds a developing agent having the same color as a color of a surface layer of the label sheet in the vicinity of the area coming into contact with the end part of the label sheet.
 7. The image forming apparatus according to claim 5, wherein the printer adds one of a yellow developing agent, a white developing agent, a colorless developing agent or a black developing agent to the area on the toner image coming into contact with the end part of the label sheet.
 8. The image forming apparatus according to claim 5, wherein the printer adds a developing agent to be decolored through heating to the area on the toner image coming into contact with the end part of the label sheet.
 9. The image forming apparatus according to claim 1, wherein the toner image at least has an image forming width having a larger width than a maximum width of the label sheet to be printed.
 10. The image forming apparatus according to claim 1, wherein the label sheet comprises a release paper, an adhesive layer and a surface layer for receiving the toner image.
 11. A label printer, comprising: a printer configured to form a toner image on a photosensitive drum; a transfer device including transfer roller configured to transfer the toner image formed on the photosensitive drum onto a label sheet; a controller configured to form the toner image on the photosensitive drum by the printer, the photosensitive drum having a width which extends over a width of the label sheet and configured to transfer the toner image onto the label sheet; and a supply device configured to supply another label sheet to the transfer device after a time passes necessary for the transfer roller to perform at least one rotation after the transfer of the toner image onto the label sheet.
 12. An image forming method, comprising: forming a toner image on a photosensitive drum; transferring the toner image formed on the photosensitive drum onto a label sheet; forming the toner image on the photosensitive drum by a printer, wherein the photosensitive drum has a width which extends over a width of the label sheet to transfer the toner image onto the label sheet; and supplying another label sheet for transferring another toner image after a time passes necessary for at least one rotation of a transfer roller after transferring the toner image onto the label sheet.
 13. The image forming method according to claim 12, further comprising: transferring a developing agent to the label sheet, and applying a bias in an opposite direction to that when transferring the toner image onto the label sheet.
 14. The image forming method according to claim 12, further comprising: transferring a developing agent to the label sheet, applying a bias in an opposite direction to that when the transferring the toner image onto the label sheet, and applying a bias in the same direction as that when transferring the toner image onto the label sheet.
 15. The image forming method according to claim 12, further comprising: adding a smaller amount of a developing agent than an area beyond the label sheet to an area at least within the label sheet in the vicinity of the area on the toner image coming into contact with the end part of the label sheet.
 16. The image forming method according to claim 15, further comprising: adding a developing agent such that a halftone visible image is formed in the area within the label sheet in the vicinity of the area on the toner image coming into contact with the end part of the label sheet.
 17. The image forming method according to claim 16, further comprising: adding a developing agent having the same color as a color of a surface layer of the label sheet in the vicinity of the area coming into contact with the end part of the label sheet.
 18. The image forming method according to claim 16, further comprising: adding one of a yellow developing agent, a white developing agent, a colorless developing agent or a black developing agent to the area on the toner image coming into contact with the end part of the label sheet.
 19. The image forming method according to claim 16, further comprising: adding a developing agent to be decolored through heating to the area on the toner image coming into contact with the end part of the label sheet.
 20. The image forming method according to claim 12, wherein the toner image at least has an image forming width having a larger width than a maximum width of the label sheet to be printed. 